Naked Science Forum

Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: Europan Ocean on 18/09/2013 10:08:30

Title: Evolution of brains and brain case?
Post by: Europan Ocean on 18/09/2013 10:08:30

Looking at the increase in size of brains in animals like humans, elephants and dolphins, which comes first, the increase in size of the brain or skull? How do the genes that change, know how to match up? Genes for skulls and genes for grey matter.

Title: Re: Evolution of brains and brain case?
Post by: evan_au on 18/09/2013 12:34:38

To some extent, the skull will grow to cover what is inside it.
Palaeontologists take a cast of the inside of the skull, which reveals major structures of the brain it once held.
A disease called hydrocephaly (http://en.wikipedia.org/wiki/Hydrocephaly#Signs_and_symptoms) results from an increase in pressure of the cerebrospinal fluid. This increased pressure can cause brain damage, but it can also cause the skull to grow abnormally large.

Title: Re: Evolution of brains and brain case?
Post by: CliffordK on 18/09/2013 21:00:00

Likely the brain and the calvarium sizes are tightly tied together.  One can't fit a bigger brain into a smaller calvarium, and a large calvarium and small brain would be wasteful.

Several cultures have done skull modifications, so presumably the brain fills the space provided.

[(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.blogiversity.org%2Fblogs%2Fcstanton%2Fmaya_skull_modification.jpg&hash=3b0de3b0106458ba32744bd53fcf2f2e)
http://www.blogiversity.org/blogs/cstanton/archive/2009/07/28/intense-body-modifications.aspx

Also consider the importance of the birth canal with respect to the head.

Likely there are several genes involved to determine the head and brain size.

Interesting thoughts about hydrocephaly. 

Another point is that the infant skull is soft, so perhaps it is designed to form around the brain to some extent.

Title: Re: Evolution of brains and brain case?
Post by: cheryl j on 19/09/2013 14:27:02

The skeleton starts off as flexible cartilage and is ossified by mineralized bone tissue, a process that starts in the womb and finishes after the baby is born. So I guess the skull can be as big as the brain  needs it to be, if it can fit through the mother's pelvic bones.

Although the idea "ontogeny recapitulates phylogeny" is somewhat discredited today, it is kind of interesting to look at what happens in development.

This article compares the speed of growth of human and chimp brains. http://www.sciencedaily.com/releases/2012/09/120924142922.htm


"Hirata and colleagues Tomoko Sakai and Hideko Takeshita now find that human and chimp brains begin to show remarkable differences very early in life. In both primate species, the brain grows increasingly fast in the womb initially. After 22 weeks of gestation, brain growth in chimpanzees starts to level off, while that of humans continues to accelerate for another two months or more. (Human gestation time is only slightly longer than that of chimpanzees, 38 weeks versus 33 or 34 weeks.)"

If there is still evolutionary pressure for bigger brains in humans, will the practice of C sections have any affect on this?